Absolute Dating Notes PDF

Absolute Dating Determining Absolute Age Absolute-age dating is a technique that enables scientists to determine the numerical age of rocks and other objects. Radioactive isotopes are used to determine the absolute age of rocks and other materials. Radioactive decay occurs as radioactive isot...

Absolute Dating Determining Absolute Age Absolute-age dating is a technique that enables scientists to determine the numerical age of rocks and other objects. Radioactive isotopes are used to determine the absolute age of rocks and other materials. Radioactive decay occurs as radioactive isotopes emit atomic particles at a constant rate. Determining Absolute Age As the number of protons changes with each emission, the original radioactive isotope, called the parent, is gradually converted to a different element, called the daughter. Determining Absolute Age Half-life is the amount of time it takes for one-half the amount of the original isotope to decay to a stable form. After one half-life, a sample contains 50% parent and 50%daughter. After two half-lives, the sample contains 25% parent and 75% daughter. Determining Absolute Age Radiometric Dating is the technique by which scientists use the ratio of parent atom to daughter atom to calculate the absolute age of the material being tested.  Determining Absolute Age Radiocarbon dating is a process that scientists use carbon-14 to determine the age of organic materials (such as fossils), which contain abundant carbon. Aging Rocks To date an igneous or metamorphic rock using radiometric dating, scientists examine the parent-daughter ratios of the radioactive isotopes in the minerals that comprise the rock. To determine the age of sedimentary rocks, scientists date layers of igneous rock or volcanic ash above and below the sedimentary layers. Alternative Absolute Dating Dendrochronology is the science of using tree rings to determine absolute age. The width of the rings depends on certain conditions in the environment. Geologists use ice-core chronologies to study glacial cycles through geologic history. Varves are bands of alternating light- and dark-colored sediments of sand, clay, and silt that accumulate at the bottom of lakes. Fossil Remains The Fossil Record Fossils provide evidence of the past existence of a wide variety of life-forms, most of which are now extinct. The diverse fossil record provides evidence that species have evolved. Evolution is the change in species over time. Formation of Fossils Fossils with original preservation are the remains of plants and animals that have been altered very little since the organisms’ deaths. Under most circumstances, the soft organic material of plants and animals decays quickly. Over time, the remaining hard parts, such as shells, bones, or cell walls, can become fossils with altered hard parts. Formation of Fossils A mold forms when sediments cover the original hard part of an organism, such as a shell, and the hard part is later removed by erosion or weathering. A cast is formed when a mold later becomes filled with a different material. Formation of Fossils Trace fossils or indirect fossils include worm trails, footprints, and tunneling burrows. Trace fossils can provide information about how an organism lived, moved, and obtained food.